Fibrous material which is used typically for acoustical or thermal insulation is commonly formed by a rotary process. Molten material such as glass, polymer material, slag, rock or basalt, is placed into a rotating spinner having a peripheral wall with orifices. The molten material is centrifuged through the orifices and formed into fibers. The fibers are attenuated and directed downwardly by the action of a flow or blast of gases discharged from an annular blower positioned circumferentially about the spinner. The downwardly moving swirling flow of fibers and gases is referred to as the veil. The fibers can be sprayed with a binder which adhesively binds the fibers together at their contact points, or the fibers can be manufactured without binder. The fibers are then collected to form a fibrous product or blanket.
A typical method of collecting the fibers includes a large hood with suction devices, such as fans, situated underneath. The fibers are collected on a foraminous conveyor positioned above the suction fans so that the suction force draws the fibers onto the conveyor. For the production of long fibers the fibers should be collected within a relatively short distance underneath the spinner, preferably within the range of from about 0.1 m to about 1.5 m. If the fibers are not collected close to the spinner the long fibers tend to bunch together and form generally parallel groupings of fibers, referred to as "ropes". This roping effect is undesirable because of the formation of a non-uniform fibrous product having areas of high density and areas of low density. For the purposes of this specification and claims, the term "long fibers" means fibers that are generally longer than about 10 inches (25 cm) as measured by the drape length method.
Ideally, the long fibers should be collected without suction or with very low amounts of suction to maintain high loft in the fibers. High amounts of suction compress the fibers and reduce the overall recovery thickness of the insulation product. However, if the fibers are collected close to the spinner on a flat foraminous conveyor with low suction, a large amount of fiber material is blown away from the conveyor and is not collected. Also, the use of suction devices is undesirable because of the high levels of noise produced, and because of the expense involved.
Another method of collecting long fibers is to use a direct formed process. The fibers are captured by two opposed conveyor surfaces. The conveyor surfaces are angled downwardly inwardly to collect and consolidate the downwardly moving veil of fibers and convert it into a flattened cross-sectional shape. The gases from the annular blower are suctioned through the conveyor surfaces, which are foraminous. The conveyor surfaces are operated in a downward direction to convey the fibers onto a second conveyor to form the fibrous insulation product. High amounts of suction are used to capture the long fibers and substantially prevent the fibers from being blown away from the conveyor and not collected.
It would be desirable to have a method of forming and collecting long fibers without the use of high suction so as to prevent the undesirable compression of the long fibers, and to produce a fibrous product that is of uniform density.